Conventionally, a glass substrate having a thickness of about 0.7 mm is generally used for a flat-screen display panel such as a liquid crystal display panel and a plasma display panel. The glass substrate of this type is desired to have a flat surface and an excellent light transmission property.
The glass substrate of this type could sometimes develop, during production, a defect such as a tiny flaw and a pore of air bubble on its surface, or a defect such as an air bubble and a foreign substance that are trapped inside of the glass substrate. If there exists such a defect, a problem that causes a scattering of light arises. In order to solve this problem, the portion where the defect exists is usually scraped off the glass substrate, and the depressed portion thus made is filled with a transparent resin and then planarized.
The defect is scraped off the glass substrate in a method using a blasting apparatus for processing the glass substrate, in which the glass substrate is struck with a high-speed blast of an abrasive (also referred to a shot or an abrasive grain) such as alumina powder, silicon carbide powder, glass beads and very small steel balls, together with fluid such as air, and the striking power causes minute destruction to the glass substrate to process the glass substrate.
FIG. 2 is a cross-sectional view showing a schematic configuration of a conventional blasting apparatus. A blasting apparatus 21 includes a blasting nozzle 22 arranged to blast an abrasive 100, and a nozzle case 23 arranged to surround the blasting nozzle 22 as shown in FIG. 2.
A suction hose 24 is connected to a posterior portion of a side wall 23a of the nozzle case 23. The suction hose 24 is arranged to collect the abrasive 100 that is blasted from the blasting nozzle 22 and used for blast processing in forming a depressed portion 200b on a surface 200a of a glass substrate 200, and thus the abrasive 100 is prevented from shattering around.
The abrasive 100 is collected because, while shattering around, it worsens a working environment and exert a harmful influence such as health damage on workers.
In this case, an abrasive having a grain diameter of several micrometers is used as the abrasive 100 blasted from the blasting nozzle 22. The depressed portion 200b that is formed by scraping a defect of the glass substrate 200 in blast processing is several millimeters in diameter, and several tens to several hundreds micrometers in depth. The prior art to the present invention is described in PTL 1.